1. Field of the Invention
This invention relates to a data processing system, and more particularly to a data processing system applied to data communication which employs serial transmission protocols between a card reader/writer and an IC card connected thereto.
2. Description of the Related Art
Recently, IC cards incorporating an IC chip have been developed as new portable data storage media, for example, as disclosed in U.S. Pat. No. 4,845,717. The IC chip includes a nonvolatile data memory and a control element such as a CPU for controlling the data memory.
The IC card is generally connected to a card reader/writer and operated in accordance with instruction data supplied from the card reader/writer. More specifically, the IC card receives instruction data from the card reader/writer and decodes a function code (instruction code) in the received instruction data. The IC card performs a process corresponding to the function code and the process result is returned to the card reader/writer as response data.
Conventionally, a block transmission protocol has been considered as a protocol for use in IC cards. In general, an IC card has a buffer memory for inputting and outputting data. When a data string longer than the size (capacity) of the buffer is to be transferred, the data string is divided into a plurality of sections, which are smaller than the buffer size, by using the known chaining function. Thereafter, the sections of the data string are successively transmitted to the IC card.
The conventional chaining function can be applied only to data transmission in one direction. For example, assume that a data string longer than the buffer size of an IC card is transmitted from a card reader/writer to the IC card, encoded in the IC card, and thereafter used in the card reader/writer. In this case, the IC card encodes sections of the data string successively supplied form the card reader/writer, and an additional memory is required to temporarily store the encoded results until all the sections of data string supplied from the card reader/writer are completed.